1. Technical Field of the Invention
The present invention relates to a shield casing with a contact piece which is soldered to the grounded part of a cable introduced in the casing.
2. Description of the Related Art
GPS (global positioning system) antenna unit is popularly employed as a positioning system. The GPS antenna for use with the GPS includes a printed circuit board with metal casing and high frequency circuit elements for processing high frequency signals. A coaxial cable is mounted to the GPS antenna such that the high frequency signals are transmitted through the coaxial cable from the high frequency circuit elements.
The GPS comprises: a GPS antenna for receiving radio waves from satellites; a high frequency circuit which subjects a high frequency signal received through the GPS antenna to noise elimination, amplification, frequency conversion, etc.; and a central processing circuit (CPU) which processes the signal which has been frequency-converted by the high frequency circuit. The GPS antenna is connected to the high frequency circuit through a coaxial cable such that only a small loss in the signal is sacrificed.
The high frequency circuit is covered with a shield structure so that it may not affect electronic equipment therearound. More specifically, the printed circuit board, on which the components of the high frequency circuit are mounted, is covered with a metal shield casing, and the latter is connected to the grounded (shielded) part of the coaxial cable. The connection of the metal shield casing to the grounded part of the coaxial cable is often achieved by soldering.
The parts FIGS. 3(A) and 3(B) are plan views showing a part of a conventional shield casing. FIG. 3(A) is a plan view showing a shield casing only. In the figure, reference numeral 11 denotes a casing body; and 12, a soldering contact piece formed by cutting the end portion of the casing body 11. FIG. 3(B) shows the grounded part 21 of a coaxial cable 20 set under the contact piece 12.
FIGS. 4(A) and 4(B) are side views showing a part of the conventional shielding casing. As shown in FIG. 4(A), the coaxial cable 20 has an insulating cover 22 inside the grounded part 21, and a central conductor 23 inside the insulating cover 22. The central conductor 23 is soldered to the conductor pattern of a printed circuit board 30. Further in FIG. 4(B), reference numeral 41 denotes a solder. The grounded part 21 is soldered to the contact piece 12 of the casing body 11. The reference numeral 42 also denotes the solder used for this soldering operation.
In the conventional shield casing shown in FIGS. 3 and 4, the contact piece 12 is flush with the casing body 11 immediately after the punching of a metal plate as shown in FIG. 3. After the contact piece 12 is bent towards the grounded part 21 in a proper angle, the contact piece 12 is welded to the latter 21 by soldering. Hence, the shield casing assembling process includes a step of bending the contact piece; that is, the number of manufacturing steps is increased as much. This is the problem to be solved by the invention.